Electric steering apparatus

ABSTRACT

A steering apparatus ( 10 ) for a vehicle having steerable wheels. The apparatus ( 10 ) comprises a rotatable vehicle steering wheel ( 12 ) and a first assembly ( 100 ) operatively coupled to the steering wheel. The first assembly ( 100 ) includes a sensor ( 30 ) for sensing applied torque and angular position of the steering wheel ( 12 ) and a first electronic control unit ( 50 ) for generating a first signal corresponding to the sensed torque and angular position of the steering wheel. A second assembly ( 100 ) is operatively coupled to the steerable wheels. The second assembly ( 100 ) includes a second electronic control unit ( 110 ) for receiving the first signal, a first electric motor ( 120 ) controlled by the second electronic control unit, and a steering gear ( 130 ) which is actuated by the first electric motor ( 120 ) to turn the steerable wheels of the vehicle. A signal transmitting conductor ( 250 ) transmits the first signal to the second electronic control unit ( 110 ).

TECHNICAL FIELD

The present invention relates to an electric steering apparatus forsteering a vehicle.

BACKGROUND OF THE INVENTION

Integral hydraulic power steering gears are commonly used in trucks,heavy equipment such as earth-moving vehicles, and constructionvehicles. “Integral” refers to a steering gear containing a manualsteering mechanism, a hydraulic control valve assembly, and a hydraulicpower cylinder integrated into a single unit.

The hydraulic power cylinder typically comprises a chamber divided intotwo chamber portions by a piston. The piston has a set of teeth whichmesh with a sector gear fixed to an output shaft. The output shaft isconnected via steering linkage to steerable wheels of a vehicle to steerthe vehicle when the output shaft is rotated.

The hydraulic control valve assembly controls the flow of pressurizedhydraulic fluid between a hydraulic pump and one of the chamber portionsto control the direction and amount of steering. The valve assemblytypically comprises two relatively rotatable valve elements, one ofwhich is connected to a rotatable input shaft operatively coupled to thevehicle steering wheel. The other valve element is connected with afollow-up member, such as a ball screw drive, which rotates in responseto movement of the piston. The ball screw drive provides a directconnection between the input shaft and the piston to allow for manualsteering of the vehicle in the event of hydraulic fluid pressure loss.

In the typical integral hydraulic power steering gear, the input shaftis connected to the vehicle steering wheel by one or more intermediateshafts. The intermediate shafts are usually long and can be prone toexcessive lash. The required routing of the intermediate shaft alsorestricts the placement of the steering gear components and othercomponents on the vehicle. It is desirable to eliminate the intermediateshaft from the vehicle steering system. If the intermediate shaft iseliminated, there is no mechanical connection between the steering wheeland the steering gear. Such systems are known, and are commonly referredto as “steer-by-wire” systems.

Because there is no mechanical connection between the steering wheel andthe steering gear, redundancy in steer-by-wire systems may be desirablefor fail-safe reasons.

It is also known to use an electrically powered steering apparatus toturn the steerable wheels instead of a hydraulically powered steeringgear. One known electric steering apparatus for turning the steerablevehicle wheels includes a ball nut for transmitting force between anelectric motor and an axially movable member. Upon actuation of theelectric motor, the ball nut is driven to rotate relative to the member.The rotational force of the ball nut is transmitted to the member byballs to drive the member axially. Axial movement of the member effectsturning movement of the steerable wheels.

In another known electric power steering apparatus, an electric motor isconnected with gearing which provides a gear reduction between anelectric motor shaft and an output pinion meshed with an axially movablemember. Rotation of the output pinion by the electric motor causes themember to move axially to turn the steerable wheels.

SUMMARY OF THE INVENTION

The present invention is a steering apparatus for a vehicle havingsteerable wheels. In accordance with one feature of the presentinvention the apparatus comprises a rotatable vehicle steering wheel anda first assembly operatively coupled to the steering wheel. The firstassembly includes a sensor for sensing applied torque and angularposition of the steering wheel and a first electronic control unit forgenerating a first signal corresponding to the sensed torque andposition of the steering wheel. A second assembly is operatively coupledto the steerable wheels. The second assembly includes a secondelectronic control unit for receiving the first signal, a first electricmotor controlled by the electronic control unit, and a hydraulicsteering gear which is actuated by the first electric motor to turn thesteerable wheels of the vehicle. A signal transmitting conductortransmits the first signal to the second electronic control unit. Inaccordance with a preferred embodiment, the first signal comprises anoptical signal and the signal transmitting conductor comprises a fiberoptic cable.

In accordance with another feature of the present invention an apparatusfor turning steerable wheels of a vehicle in response to turning of asteering wheel of the vehicle comprises a sensor for sensing steeringwheel torque/position and for providing a first output signal indicativeof steering wheel torque/position. A steering gear is actuatable to turnat least one steerable wheel of the vehicle. A dual drive electric motoris energizable to actuate the steering gear. The motor has a first setof windings and a second set of windings. The first set of windingsenergizes the motor to actuate the steering gear independent of thesecond set of windings. The second set of windings energizes the motorto actuate the steering gear independent of the first set of windings.An electronic control unit receives the first output signal and controlselectrical current flow through the first and second sets of windings.

In accordance with yet another feature of the present invention anapparatus comprises a rotatable vehicle steering wheel and a firstassembly operatively coupled to the steering wheel. The first assemblyincludes a sensor for sensing applied torque and angular position of thesteering wheel and a first electronic control unit for generating afirst signal corresponding to the aforementioned parameters. A secondassembly is operatively coupled to the steerable wheels. The secondassembly includes a second electronic control unit for receiving thefirst signal, a first electric motor controlled by the second electroniccontrol unit, and a steering gear which is actuated by the firstelectric motor to turn the steerable wheels of the vehicle. The steeringgear includes an axially movable member and a rotatable ball nutrotatable by the first electric motor. Rotation of the ball nuttransmits force to the axially movable member to axially move themovable member to turn the steerable wheels. A signal transmittingconductor transmits the first signal from the first electronic controlunit to the second electronic control unit. Preferably, the first signalcomprises an optical signal and the signal transmitting conductorcomprises a fiber optic cable.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to one skilled in the art to which the present inventionrelates upon reading the following description of the invention withreference to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of a vehicle steering apparatusconstructed in accordance with the present invention;

FIG. 2 is a sectional view through a component of the steering apparatusof FIG. 1.

FIG. 3 is a schematic block diagram of a vehicle steering apparatusconstructed in accordance with a second embodiment of the presentinvention;

FIG. 4 is a schematic sectional view of a component of the steeringapparatus of FIG. 3.

FIG. 5 is another schematic block diagram of the steering apparatus ofFIG. 3; and

FIG. 6 is a sectional view of another component of the steeringapparatus of FIG. 3.

FIG. 7 is a schematic block diagram of a vehicle steering apparatusconstructed in accordance with another embodiment of the presentinvention;

FIG. 8 is a schematic sectional view of a component of the apparatus ofFIG. 7; and

FIG. 9 is a sectional view through another component of the steeringapparatus of FIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is an electric steering apparatus for steering avehicle. As representative of an embodiment of the present invention,FIG. 1 schematically illustrates a steering apparatus 10. The steeringapparatus 10 comprises a vehicle steering wheel 12, a first assembly 20,a second assembly 100 operatively coupled to steerable wheels (notshown) of a vehicle, and a signal transmitting conductor 250 extendingbetween the first and second assemblies. The vehicle steering wheel 12is of known construction and is manually rotatable by a vehicleoperator. The first assembly 20 is operatively coupled to the vehiclesteering wheel 12 in a known manner (not shown).

The first assembly 20 includes a torque/position sensor 30, an electricmotor 40, and a first electronic control unit 50. These three componentsof the first assembly 20 are integrated into a single unit. Thetorque/position sensor 30, shown only schematically in FIG. 1, isoperable to sense applied torque and rotation of the steering wheel 12by the operator. The torque/position sensor 30 preferably comprises anoptical sensor having relatively rotatable first and second disks (notshown). Two sets of light emitters (not shown) are positioned to emitlight toward the disks. Two sets of light receivers (not shown) arepositioned to receive light that shines through the disks. The sensor 30is able to determine the applied torque to the steering wheel and theangular position of the steering wheel based on the received light. Itis contemplated that the torque/position sensor 30 could be some othertype of sensor, rather than an optical sensor. It is furthercontemplated that the first assembly 20 could include one or moreadditional torque/position sensors 30 in order to have redundancy incase a problem develops with the primary position sensor.

The electric motor 40, hereinafter referred to as the steering feelmotor, is operatively coupled to the steering wheel 12 to provideresistance to rotation of the steering wheel and thereby providesteering feel to the vehicle operator. The steering feel motor 40 iscontrolled by the first electronic control unit 50 in response tosignals received from the second assembly 100 as described furtherbelow.

The electronic control unit 50 is operable to generate a first signalcorresponding to the sensed torque and angular rotation of the steeringwheel 12 sensed by the torque/position sensor 30. Further, the firstelectronic control unit 50 has multiplexing capability and is operableto send the first signal to the second assembly 100 via the signaltransmitting conductor 250. Preferably, the first signal is an opticalsignal and the signal transmitting conductor 250 is a high speed fiberoptic cable.

The second assembly 100 includes a second electronic control unit 110,an electric motor 120, and a hydraulic power steering gear 130 forturning the steerable wheels to effect steering of the vehicle. Thesethree components of the second assembly 100 are integrated into a singleunit in order to minimize the number of electrical contacts and maximizereliability. The second electronic control unit 110 is operable toreceive the first signal transmitted by the fiber optic cable 250. Thesecond electronic control unit 110 is further operable to control theelectric motor 120 based on the first signal. The electric motor 120 hasan output shaft (not shown) which drives the hydraulic steering gear130.

The steering gear 130 is an integral hydraulic power steering gear andincludes a two-piece housing 132 (FIG. 2) having a hydraulic powercylinder 134. The power cylinder 134 comprises a chamber 136 dividedinto two chamber portions 138 and 140, respectively, by a piston 142.The piston 142 includes an inner bore 143 with a helical groove 144. Thepiston 142 also has a set of external teeth 145 which mesh with a sectorgear 146. The sector gear 146 is fixed to an output shaft 148 whichextends outwardly from the housing 132. The output shaft 148 isconnected to a pitman arm (not shown) which, in turn, is connected viasteering linkage (not shown) to the steerable wheels to steer thevehicle. As the piston 142 moves in the chamber 136, the output shaft148 is rotated to operate the steering linkage, which turns thesteerable wheels of the vehicle.

A hydraulic control valve assembly 150 controls the flow of pressurizedhydraulic fluid between a hydraulic circuit including a hydraulic pump(not shown) and one of the chamber portions 138 and 140 to control thedirection and amount of steering. The valve assembly 150 is actuated bya rotatable input shaft 152. The input shaft 152 is rotated by theelectric motor 120.

The valve assembly 150 comprises first and second valve members 154 and156, respectively. The first valve member 154 comprises a valve core 160and the second valve member 156 comprises a valve sleeve 162. The valvecore 160 is located coaxially within the valve sleeve 162 and issupported for rotation by the valve sleeve. The valve core 160 is formedintegrally as one piece with the input shaft 152. The valve core 160 hasoppositely disposed first and second end portions 164 and 166,respectively, and a valve section 168 between the end portions. Thefirst end portion 164 of the valve core 160 projects beyond the valvesleeve 162 and the second end portion 166 of the valve core lies withinthe valve sleeve.

The valve section 168 of the valve core 160 has a plurality ofcircumferentially spaced, axially extending grooves 170 as is known inthe art. A first portion of the grooves 170 are fluidly connected withan internal passage 172 extending from the valve section 168 of thevalve core 160 to the second end portion 166. The internal passage 172communicates via passages (not shown) with the return line of ahydraulic pump circuit (not shown). A second portion of the grooves 170are in fluid communication with a plurality of passages 174 in the valvesleeve 162.

The valve sleeve 162 has oppositely disposed first and second ends 180and 182, respectively. The valve sleeve 162 further includes a sleevesection 184 adjacent the first end 180 and a ball screw section 186adjacent the second end 182. An axially extending passage 188 extendsfrom the first end 180 of the valve sleeve 162 through the sleevesection 184 and the ball screw section 186 to the second end 182.

The first end 180 of the valve sleeve 162 includes first and second lugs(not shown) that are disposed in diametrically opposed cut-outs (notshown) in the valve core 160. Upon rotation of the valve core 160 ofbetween 2° and 8° relative to the valve sleeve 162, the lugs engage thecut-outs in the valve core to cause the valve sleeve to be rotated alongwith the valve core. Such rotation of the valve sleeve 162 causes thepiston 142 to move axially in the chamber 136 and, hence, allows formanual steering of the vehicle even if a loss in hydraulic fluidpressure has occurred.

The sleeve section 184 of the valve sleeve 162 includes the plurality ofpassages 174 (FIG. 2) which extend from the outer circumference of thesleeve section to the inner circumference. The passages 174 communicatewith an annular chamber 190 in the housing 132 which is fluidlyconnected to the hydraulic pump. A plurality of axially extendinggrooves 192 are formed in the inner surface of the valve sleeve 162 asis known in the art. The grooves 192 fluidly communicate with the secondportion of the grooves 170 in the valve core 160. Further, a firstportion of the grooves 192 in the valve sleeve 162 are fluidly connectedvia passages (not shown) with the first chamber portion 138 in thehousing 132, and a second portion of the grooves 192 fluidly connectedvia passages (not shown) with the second chamber portion 140 in thehousing. As is known in the art, when the valve core 160 is rotatedrelative to the valve sleeve 162, hydraulic fluid is ported through thegrooves 170 and 192 and associated passages to one of the chamberportions 138 and 140, while the hydraulic fluid is vented from the otherchamber portion, thereby causing the piston 132 to move accordingly.

The ball screw section 186 of the valve sleeve 162 includes a helicalgroove 194 formed on its outer periphery. A plurality of balls 196 arelocated in the helical groove 140. The balls 196 are also located in thehelical groove 144 in the bore 143 formed in the piston 142. As is wellknown in the art, axial movement of the piston 142 causes the ball screwportion 186 to rotate which, in turn, causes the rest of the valvesleeve 162 to rotate.

A torsion bar 198 connects the valve core 160 and the valve sleeve 162.One end of the torsion bar 198 is connected by a pin 200 to the valvesection 168 of the valve core 160, while the other end of the torsionbar extends through the passage 188 in the valve sleeve 162 and isconnected by a pin 202 adjacent the second end 182 of the valve sleeve.

The hydraulic steering gear 130 further includes a plurality of outputposition sensors 210 for sensing rotation of the output shaft 148. Theposition sensors 210 are non-contacting position sensors. Multipleoutput position sensors 210 are used for redundancy purposes. The secondelectronic control unit 110 is operable to generate a second signalcorresponding to the rotation of the steering gear output shaft 148sensed by the position sensors 210. Further, the second electroniccontrol unit 110 has multiplexing capability and is operable to send thesecond signal to the first assembly 30 via the fiber optic cable 250. Inaccordance with the preferred embodiment, the second signal is anoptical signal.

The second signal is received by the first electronic control unit 50.The first electronic control unit 50 controls the steering feel motor 40in response to the second signal. The multiplexing capability of thefirst and second electronic control units 50 and 110 allows the firstand second signals to be transmitted practically simultaneously usingthe fiber optic cable 250. The electronic control units 50 and 110 canvary the intensity of the first and second signals and/or thefrequency/phase of the signals in order to constantly exchange signalinformation during operation of the vehicle.

The second signal thus provides feedback to the vehicle operator, in theform of resistance to rotation of the steering wheel 12 by the steeringfeel motor 40, of the actual position of the steerable wheels uponmanual rotation of the steering wheel. In addition, the first electroniccontrol unit 50 could be programmed to increase the resistance torotation of the steering wheel 12 with vehicle speed.

It is contemplated that the apparatus 10 could include one or moreadditional assemblies, similar to the second assembly 100, so that eachsteerable wheel has its own steering gear 130 in order to provide“perfect Ackermann” steering.

From the above description of the embodiment of FIGS. 1-2, those skilledin the art will perceive improvements and changes. For example, ordinaryelectrical signals and appropriate wiring could be used to exchangesteering position information between the first and second assemblies inplace of the optic signals and fiber optic cable discussed above. Also,instead of the plurality of output position sensors 210 for sensingrotation of the output shaft, a plurality of sensors (not shown) may beused to sense the rotation of the input shaft 152.

As representative of a second embodiment of the present invention, FIG.3 schematically illustrates a steering apparatus 300. The steeringapparatus 300 comprises a vehicle steering wheel 301, a torque/positionsensor 302, an electronic control unit 303, an electric motor 304, asteering gear 305, and steerable wheels 306 (FIG. 5). The steeringapparatus 300 is a steer-by-wire system. Thus, there is no mechanicalconnection between the steering wheel 301 and the steering gear 305 asis described below.

The steering wheel 301 is manually rotatable by a vehicle driver toinitiate turning of the vehicle. The torque/position sensor 302 isoperatively coupled with the steering wheel 301. The torque/positionsensor 302 is operable to sense applied torque and angular position ofthe steering wheel 301 and to generate a first signal indicative of theaforementioned parameters. The torque/position sensor 302 preferablycomprises a known optical sensor, but could alternatively compriseanother suitable type of sensor. It is contemplated that the apparatus300 could include a second torque/position sensor 302 for redundancypurposes.

The electronic control unit (ECU) 303 is operatively coupled with thetorque/position sensor 302 and receives the first signal. The ECU 303includes first and second power supplies 310 and 312 (FIG. 3) forredundancy purposes. The power supplies 310 and 312 are operativelycoupled in parallel with a vehicle battery 314 and a vehicle ground 316.The ECU 303 further includes first and second drive circuits 318 and320. The ECU 303, through one or both of the drive circuits 318 and 320,controls the flow of electrical current to the electric motor 304 basedon the first signal.

The electric motor 304 is a three phase brushless motor having a rotor324 (FIG. 4) and a stator 326. An output shaft 328 (FIG. 3) is connectedto one end of the rotor 324. A first set of permanent magnets 330 aremounted on the rotor 324 and extend in an annular array. A second set ofpermanent magnets 332 also extend in an annular array about the rotor324. The second set of magnets 332 is spaced axially from the first setof magnets 330.

A first set of windings 336 is secured to the stator 326 in the electricmotor 304. The first set of windings 336 align radially with the firstset of magnets 330 on the rotor 324. The first set of windings 336 areenergizable by current from the first drive circuit 318 in the ECU 303to cause the rotor 324 to rotate. A second set of windings 340 issecured to the stator 326 in the electric motor 304. The second set ofwindings 340 align radially with the second set of magnets 332 on therotor 324. The second set of windings 340 are energizable by currentfrom the second drive circuit 320 in the ECU 303 to cause the rotor 324to rotate. The first and second sets of windings 336 and 340 can beindependently energized by the first and second drive circuits 318 and320, respectively, and thus provide the electric motor 304 with dualdrive capability, with the ECU 303 providing electronic commutation.

The steering gear 305 is an integral hydraulic power steering gearsimilar to the steering gear of FIG. 2 and the same reference numbersused in describing the steering gear of FIG. 2 are used to describe thesteering gear of FIG. 6. The steering gear of FIG. 6 includes atwo-piece housing 132 (FIG. 6) having a hydraulic power cylinder 134.The power cylinder 134 comprises a chamber 136 divided into two chamberportions 138 and 140, respectively, by a piston 142. The piston 142includes an inner bore 143 with a helical groove 144. The piston 142also has a set of external teeth 145 which mesh with a sector gear 146.The sector gear 146 is fixed to an output shaft 148 which extendsoutwardly from the housing 132. The output shaft 148 is connected to apitman arm 125 (FIG. 3) which, in turn, is connected via steeringlinkage (not shown) to the steerable wheels to steer the vehicle. As thepiston 142 moves in the chamber 136, the output shaft 148 is rotated tooperate the steering linkage, which turns the steerable wheels of thevehicle.

A hydraulic control valve assembly 150 controls the flow of pressurizedhydraulic fluid between a hydraulic circuit including a hydraulic pump(not shown) and one of the chamber portions 138 and 140 to control thedirection and amount of steering. The valve assembly 150 is actuated bythe shaft 102 of the electric motor 100.

The valve assembly 150 comprises first and second valve members 154 and156, respectively. The first valve member 154 comprises a valve core 160and the second valve member 156 comprises a valve sleeve 162. The valvecore 160 is located coaxially within the valve sleeve 162 and issupported for rotation by the valve sleeve. The valve core 160 is formedintegrally as one piece with the input shaft 152. The valve core 160 hasoppositely disposed first and second end portions 164 and 166,respectively, and a valve section 168 between the end portions. Thefirst end portion 164 of the valve core 160 projects beyond the valvesleeve 162 and the second end portion 166 of the valve core lies withinthe valve sleeve.

The valve section 168 of the valve core 160 has a plurality ofcircumferentially spaced, axially extending grooves 170 as is known inthe art. A first portion of the grooves 170 are fluidly connected withan internal passage 172 extending from the valve section 168 of thevalve core 160 to the second end portion 166. The internal passage 172communicates via passages (not shown) with the return line of ahydraulic pump circuit (not shown). A second portion of the grooves 170are in fluid communication with a plurality of passages 174 in the valvesleeve 162.

The valve sleeve 162 has oppositely disposed first and second ends 180and 182, respectively. The valve sleeve 162 further includes a sleevesection 184 adjacent the first end 180 and a ball screw section 186adjacent the second end 182. An axially extending passage 188 extendsfrom the first end 180 of the valve sleeve 162 through the sleevesection 184 and the ball screw section 186 to the second end 182.

The first end 180 of the valve sleeve 162 includes first and second lugs(not shown) that are disposed in diametrically opposed cut-outs (notshown) in the valve core 160. Upon rotation of the valve core 160 ofbetween 2° and 8° relative to the valve sleeve 162, the lugs engage thecut-outs in the valve core to cause the valve sleeve to be rotated alongwith the valve core. Such rotation of the valve sleeve 162 causes thepiston 142 to move axially in the chamber 136 and, hence, allows formanual steering of the vehicle even if a loss in hydraulic fluidpressure has occurred.

The sleeve section 184 of the valve sleeve 162 includes the plurality ofpassages 174 which extend from the outer circumference of the sleevesection to the inner circumference. The passages 174 communicate with anannular chamber 190 in the housing 132 which is fluidly connected to thehydraulic pump. A plurality of axially extending grooves 192 are formedin the inner surface of the valve sleeve 162 as is known in the art. Thegrooves 192 fluidly communicate with the second portion of the grooves170 in the valve core 160. Further, a first portion of the grooves 192in the valve sleeve 162 are fluidly connected via passages (not shown)with the first chamber portion 138 in the housing 132, and a secondportion of the grooves 192 fluidly connected via passages (not shown)with the second chamber portion 140 in the housing. As is known in theart, when the valve core 160 is rotated relative to the valve sleeve162, hydraulic fluid is ported through the grooves 170 and 192 andassociated passages to one of the chamber portions 138 and 140, whilethe hydraulic fluid is vented from the other chamber portion, therebycausing the piston 132 to move accordingly.

The ball screw section 186 of the valve sleeve 162 includes a helicalgroove 194 formed on its outer periphery. A plurality of balls 196 arelocated in the helical groove 140. The balls 196 are also located in thehelical groove 144 in the bore 143 formed in the piston 142. As is wellknown in the art, axial movement of the piston 142 causes the ball screwportion 186 to rotate which, in turn, causes the rest of the valvesleeve 162 to rotate.

A torsion bar 198 connects the valve core 160 and the valve sleeve 162.One end of the torsion bar 198 is connected by a pin 200 to the valvesection 168 of the valve core 160, while the other end of the torsionbar extends through the passage 188 in the valve sleeve 162 and isconnected by a pin 202 adjacent the second end 182 of the valve sleeve.

The hydraulic steering gear 130 further includes a plurality of outputposition sensors 210 (FIG. 5) for sensing rotation of the output shaft148. The position sensors 210 are of the non-contacting type having noparts which slidingly engage each other. There are multiple outputposition sensors 210 for redundancy purposes. The position sensors 210generate a second signal corresponding to the rotation of the steeringgear output shaft 148 and provide the second signal to the ECU 303. TheECU 303 compares the second signal to the first signal and adjusts thecontrol of the electric motor 304 depending on the position of thesteerable wheels 306 versus the position that the steering wheel 301 iscommanding the steerable wheels to take.

The steering apparatus 300 disclosed above has redundant power supplies310 and 312, redundant drive circuits 318 and 320 which controlredundant windings 336 and 340, respectively, in an electric motor, andredundant output position sensors 210 to provide the steering apparatuswith fail-safe capability.

As representative of another embodiment of the invention, FIG. 7schematically illustrates a steering apparatus similar to the steeringapparatus of FIG. 1. Reference numbers used in FIG. 1 are used in FIG. 7to designate corresponding parts. As shown in FIG. 7, a steeringapparatus 10 comprises a vehicle steering wheel 12, a first assembly 20,a second assembly 100 operatively coupled to steerable wheels (notshown) of a vehicle, and a signal transmitting conductor 250 extendingbetween the first and second assemblies. The vehicle steering wheel 12is of known construction and is manually rotatable by a vehicleoperator. The first assembly 20 is operatively coupled to the vehiclesteering wheel 12 in a known manner (not shown).

The first assembly 20 includes a torque/position sensor 30, an electricmotor 40, and a first electronic control unit (ECU) 50. These threecomponents of the first assembly 20 are integrated into a single unit.The torque/position sensor 30, shown only schematically in FIG. 7, isoperable to sense applied torque and angular position of the steeringwheel 12 by the operator. The torque/position sensor 30 preferablycomprises an optical sensor having relatively rotatable first and seconddisks (not shown). Two sets of light emitters (not shown) are positionedto emit light toward the disks. Two sets of light receivers (not shown)are positioned to receive light that shines through the disks. Thesensor 30 is able to determine the amount of torque applied to thesteering wheel and the angular position of the steering wheel based onthe received light. It is contemplated that the torque/position sensor30 could be some other type of sensor, rather than an optical sensor. Itis further contemplated that the first assembly 20 could include one ormore additional torque/position sensors 30 for redundancy in case aproblem develops with the primary sensor.

The electric motor 40, hereinafter referred to as the steering feelmotor, is operatively coupled to the steering wheel 12 to provideresistance to rotation of the steering wheel and thereby providesteering feel to the vehicle operator. The steering feel motor 40 iscontrolled by the first ECU 50 in response to signals received from thesecond assembly 100 as described further below.

The first ECU 50 is operatively coupled with the torque/position sensor30 and generates a first signal corresponding to the applied torque andangular position of the steering wheel 12 sensed by the torque/positionsensor 30. Further, the first ECU 50 has multiplexing capability and isoperable to send the first signal to the second assembly 100 via thesignal transmitting conductor 250. Preferably, the first signal is anoptical signal and the signal transmitting conductor 250 is a high speedfiber optic cable.

The second assembly 100 includes a second electronic control unit (ECU)110, an electric motor 120, and a power steering gear 130 for turningthe steerable wheels to effect steering of the vehicle. These threecomponents of the second assembly 100 are integrated into a single unitin order to minimize the number of electrical contacts and maximizereliability. The second ECU 110 is operable to receive the first signaltransmitted by the fiber optic cable 250. The second ECU 110 includesfirst and second drive circuits 90 and 92. The second ECU 110, throughone or both of the drive circuits 90 and 92, controls the flow ofelectrical current to the electric motor 120 based on the first signal.

The electrical motor 120 is a three phase brushless motor having a rotor401 (FIG. 8) and a stator 402. An output shaft 403 (FIG. 9) is connectedto one end of the rotor 401. A first set of permanent magnets 406 aremounted on the rotor and extend in an annular array. A second set ofpermanent magnets 407 also extend in an annular array about the rotor401. The second set of magnets 407 is spaced axially from the first setof magnets 406.

A first set of windings 408 is secured to the stator 408 in the electricmotor 120. The first set of windings 408 align radially with the firstset of magnets 406 on the rotor 401. The first set of windings 408 areenergizable by current from the first drive circuit 90 in the second ECU110 to cause the rotor 401 to rotate. A second set of windings 409 issecured to the stator 402 in the electric motor 120. The second set ofwindings 409 align radially with the second set of magnets 407 on therotor 401. The second set of windings 409 are energizable by currentfrom the second drive circuit 92 in the second ECU 110 to cause therotor 401 to rotate. The first and second sets of windings 408 and 409can be independently energized by the first and second drive circuits 90and 92, respectively, and thus provide the electric motor 120 with dualdrive capability, with the second ECU 110 providing electroniccommutation.

The steering gear 130 includes a linearly movable steering member 432(FIG. 9) that extends axially through a housing 431. The steering member432 is linearly (or axially) movable along an axis 434. The steeringmember 432 includes a screw portion 440 having an external threadconvolution. The steering member 432 is connected with steerable wheels(also not shown) of the vehicle through tie rods 442 located at thedistal ends of the steering member. Linear movement of the steeringmember 432 along the axis 434 results in steering movement of thesteerable wheels as is known in the art.

The housing 431 has a generally cylindrical configuration including anaxially extending side wall 450 centered on the axis 434. A radiallyenlarged section 452 of the housing 431 is located at the right end (asviewed in FIG. 9) of the housing 431. The radially enlarged section 452of the housing 431 defines an annular chamber 454. An outboard housing458 is attached, in a manner not shown, to the radially enlarged section452 of the housing 431 and closes the chamber 454.

A ball nut assembly 470 is located in the chamber 454 in the radiallyenlarged section 452 of the housing 431 and encircles the screw portion440 of the steering member 432. The ball nut assembly 470 includes aball nut 472, a plurality of force transmitting members 474, a firstbearing assembly 476, a gear member 478, and a lock nut 480. The locknut 480 screws onto the ball nut 472 to axially secure the parts of theball nut assembly 470.

The plurality of force-transmitting members 474 comprise balls disposedbetween the internal screw thread convolution of the ball nut 472 andthe external thread convolution on the screw portion 440 of the steeringmember 432. The ball nut assembly 470 includes a recirculation passage(not shown) for recirculating the balls upon axial movement of thesteering member 432 relative to the ball nut assembly. The ball nutassembly 470 provides a gear reduction ratio as is known in the art.

The electric motor 120 is mounted to a radially extending gearboxportion 422 of the housing 431. The gearbox portion 422 extends from theradially enlarged section 452 of the housing 431. The gearbox portion422 contains meshed first and second gears 424 and 426, respectively.The first gear 424 is the gear member 478 of the ball nut assembly 470.The second gear 426 is connected for rotation with the motor outputshaft 403 extending from the electric motor 120. The meshed first andsecond gears 424 and 426 provide a gear reduction ratio between themotor output shaft 103 of the electric motor 120 and the ball nutassembly 470. When the gear reduction ratio of the ball nut assembly 470is combined with the gear reduction ratio of the gears 424 and 426, anoverall gear reduction ratio for the steering assembly 10 is provided.

In the illustrated embodiment of the invention, the motor 120 extendstransverse to the steering member 432 at a right angle. It iscontemplated, however, that the motor 120 could lie parallel to thesteering member 432 or at a different angle, such as 45°, relative tothe steering member.

The steering gear 130 further includes a plurality of output positionsensors 210, illustrated schematically in FIGS. 7 and 9, for sensing theamount of rotation of the ball nut 470. The position sensors 210 areshown in FIG. 7 as part of the second assembly 100. The position sensors210 are non-contacting sensors. There are a multiplicity of outputposition sensors 210 for redundancy purposes. The second ECU 110 isoperable to generate a second signal corresponding to the rotation ofthe ball nut 470 sensed by the position sensors 210. Further, the secondECU 110 has multiplexing capability and is operable to send the secondsignal to the first assembly 30 via the fiber optic cable 250.Preferably, the second signal is an optical signal.

The second signal is received by the first ECU 50. The first ECU 50controls the steering feel motor 40 in response to the second signal.The multiplexing capability of the first and second electronic controlunits 50 and 110 allows the first and second signals to be transmittedpractically simultaneously using the fiber optic cable 250. Theelectronic control units 50 and 110 can vary the intensity of the firstand second signals and/or the frequency phase of the signals in order toconstantly exchange signal information during operation of the vehicle.

The second signal thus provides feedback to the vehicle operator, in theform of resistance to rotation of the steering wheel 12 by the steeringfeel motor 40, of the actual position of the steerable wheels uponmanual rotation of the steering wheel. In addition, the first ECU 50could be programmed to increase the resistance to rotation of thesteering wheel 12 with vehicle speed.

It is contemplated that the apparatus 10 could include one or moreadditional assemblies, similar to the second assembly 100, so that eachsteerable wheel has its own steering gear 130 in order to provide“perfect Ackermann” steering.

From the above description of the embodiment of FIGS. 7-9, those skilledin the art will perceive improvements, changes and modifications. Forexample, ordinary electrical signals and appropriate wiring could beused to exchange steering position information between the first andsecond assemblies in place of the optic signals and fiber optic cablediscussed above. Such improvements, changes and modifications within theskill of the art are intended to be covered by the appended claims.

1. An apparatus for turning steerable wheels of a vehicle in response toturning of a steering wheel of the vehicle, said apparatus comprising: afirst assembly operatively connected to the steering wheel, said firstassembly including a sensor apparatus which senses torque applied to thesteering wheel and an angular position of the steering wheel, a firstelectric motor operatively coupled with the steering wheel to provideresistance to rotation of the steering wheel, and a first electroniccontrol unit connected with said first electric motor, said firstelectronic control unit is operable to generate a first optical signalwhich is a function of the sensed torque applied to the steering wheeland the sensed angular position of the steering wheel; a second assemblyoperatively coupled to a steering mechanism connected with the steerablewheels of the vehicle, said second assembly including a sensor apparatuswhich is connected with the steering mechanism and is operable to sensea position of a portion of the steering mechanism connected to thesteerable vehicle wheels to thereby sense a position of the steerablevehicle wheels, a second electric motor which is connected with thesteering mechanism and is operable to effect operation of the steeringmechanism to change the position of the steerable vehicle wheels, and asecond electronic control unit connected with said second electricmotor, said second electronic control unit is operable to generate asecond optical signal which is a function of the sensed position of saidportion of the steering mechanism; and a fiber optic cable connectedwith said first and second electronic control units, said fiber opticcable is effective to conduct said first optical signal from said firstelectronic control unit to said second electronic control unit to enablesaid second electronic control unit to control operation of said secondelectric motor as a function of the sensed torque applied to thesteering wheel and the sensed angular position of the steering wheel,said fiber optic cable is effective to conduct said second opticalsignal from said second electronic control unit to said first electroniccontrol unit to enable said first electronic control unit to controloperation of said first electric motor as a function of the position ofsaid portion of the steering mechanism.
 2. An apparatus as set forth inclaim 1 wherein said first and second electronic control units havemultiplexing capabilities to enable said first electronic control unitto send the first optical signal which is a function of the sensedtorque applied to the steering wheel and the sensed angle of rotation ofthe steering wheel over said fiber optic cable to said second electroniccontrol unit while said second electronic control unit is sending thesecond optical signal which is a function of the sensed position of saidportion of the steering mechanism over said fiber optic cable to saidfirst electronic control unit.
 3. An apparatus as set forth in claim 2wherein said second electric motor is a dual drive electric motor havinga rotor with first and second sets of permanent magnets which arerotatable together about an axis of rotation of said second electricmotor and a stator which extends around said rotor and includes firstand second sets of windings, said first set of windings extends aroundsaid first set of permanent magnets and said second set of windingsextends around said second set of permanent magnets.
 4. An apparatus asset forth in claim 3 wherein said second electronic control unitincludes a first motor drive circuit which is operable to directelectrical current to said first set of windings and a second motordrive circuit which is operable to direct electrical current to saidsecond set of windings.
 5. An apparatus for turning steerable wheels ofa vehicle in response to turning of a steering wheel of the vehicle,said apparatus comprising: a steering mechanism connected with thesteerable vehicle wheels, said steering mechanism includes an axiallymovable steering member and a ball nut which is rotatable about alongitudinal central axis of said steering member; a first assemblyoperatively connected to the steering wheel, said first assemblyincluding a sensor apparatus which senses torque applied to the steeringwheel and an angular position of the steering wheel, a first electricmotor operatively coupled with the steering wheel to provide resistanceto rotation of the steering wheel, and a first electronic control unitconnected with said first electric motor, said first electronic controlunit is operable to generate a first signal which is a function of thesensed torque applied to the steering wheel and the sensed angularposition of the steering wheel; a second assembly connected with saidfirst assembly and operatively coupled to said steering mechanism, saidsecond assembly including a sensor apparatus which is connected with thesteering mechanism and is operable to sense a position of a portion ofthe steering mechanism connected to the steerable vehicle wheels tothereby sense a position of the steerable vehicle wheels, a secondelectric motor which is connected with the steering mechanism and isoperable to effect operation of the steering mechanism to change theposition of the steerable vehicle wheels, and a second electroniccontrol unit connected with said second electric motor, said secondelectronic control unit is operable to generate a second signal which isa function of the sensed position of said portion of the steeringmechanism; and a signal conductor connected with said first and secondelectronic control units, said signal conductor is effective to conductsaid first signal from said first electronic control unit to said secondelectronic control unit to enable said second electronic control unit tocontrol operation of said second electric motor as a function of thesensed torque applied to the steering wheel and the sensed angularposition of the steering wheel, said signal conductor is effective toconduct said second signal from said second electronic control unit tosaid first electronic control unit to enable said first electroniccontrol unit to control operation of said first electric motor as afunction of the position of said portion of the steering mechanism, saidsecond electric motor is a dual drive electric motor having a rotor withfirst and second sets of permanent magnets which are rotatable togetherabout an axis of rotation which extends transverse to a central axis ofsaid steering member and a stator which extends around said rotor andincludes a first set of windings which extends around said first set ofpermanent magnets and a second set of windings which extends around saidsecond set of permanent magnets, said second electronic control unitincludes a first motor drive circuit which is operable to directelectrical current to said first set of windings to effect rotation ofsaid rotor about the axis of rotation which extends transverse to thecentral axis of said steering member and a second motor drive circuitwhich is operable to direct electrical current to said second set ofwindings to effect rotation of said rotor about the axis of rotationwhich extends transverse to the central axis of said steering member. 6.An apparatus as set forth in claim 5 wherein said signal conductor is afiber optic cable, said first and second electronic control units havemultiplexing capabilities to enable said first electronic control unitto send the first signal over said fiber optic cable to said secondelectronic control unit while said second electronic control unit issending the second signal over said fiber optic cable to said firstelectronic control unit.